Navy Yard shooter Aaron Alexis’ ability to get a national security clearance despite a history of arrests, questions about mental illness, and a spotty Navy record looms as a major question the day after the mass shooting that left the 34 year old and 12 others dead.

“It really is hard to believe that someone with a record as checkered as this man could conceivably get, you know, clearance,” Washington D.C. Mayor Vincent Gray said in an interview with CNN.

But an arrest history or even convictions do not automatically disqualify someone from getting a national security clearance, records show.

While the names of the applicants aren’t public, a quick perusal of the rulings shows applicants with criminal pasts.

Take the case of one man who had a fairly extensive record of convictions, including public intoxication and drug conspiracy charges more than a decade ago that resulted in a prison sentence.

After a hearing, an administrative judge at the Defense Department issued a ruling calling the applicant a hard working man who didn’t deny his background and mistakes, but who proved he was suitable for a security clearance.

In another case, an applicant had a history of alcohol-fueled criminal behavior. He was convicted of assault on a police officer in 2001 and assault with a deadly weapon two years later. Over the next few years, he faced disorderly conduct, public intoxication, vandalism and drunk driving charges.

The government deemed him ineligible for a clearance. But the applicant said he quit drinking years ago and had gotten his life back together, vowing never to drink again. A judge ruled against the government, ruling him eligible for a clearance.

There’s no indication that Alexis’ application faced any such hurdles.

The government contractor that hired Alexis told the Washington Post that officials knew nothing about reports of gun-related arrests involving their employee.

“If I can find this out just by doing a Google search, that is sad,” Thomas Hoshko, chief executive of The Experts, told The Post. “Anything that suggests criminal problems or mental health issues, that would be a flag. We would not have hired him.”

Meanwhile, the Navy Yard rampage has raised broader concerns about security at military installations. On Tuesday, the Pentagon’s Inspector General released a report showing that 52 convicted felons had received routine, unauthorized access to Navy installations.

Greg Rinckey, a former Judge Advocate General attorney who represents clients on security clearance issues, said in an interview that Alexis’ background should’ve been vetted more closely.